This invention is generally directed to frequency synthesizer modules of the type which conventionally include interconnected signal controlled oscillator (e.g. a VCO) and phase locked loop (PLL) circuit sub-assemblies. Although such sub-assemblies must be electrically connected at some points in the circuit (in accordance with well known and conventional principles), it is desirable for other reasons to maintain electrical isolation otherwise between these two circuit sub-assemblies. At the same time, the frequency synthesizer module must be mechanically robust yet easily disassembled for troubleshooting and/or servicing purposes.
Although there is a considerable body of prior art related to the electrical and physical mounting of circuit sub-assemblies as well as their electrical isolation and interconnection, there has in the past been a continuing need for an improved arrangement of physical and electrical interconnections and shielding in frequency synthesizer modules using VCO and PLL sub-assemblies and designed, for example, for use in mobile radios or the like where the arrangement needs to be especially robust and serviceable.
As those in the art will appreciate, the use of conductive walls to electrically shield one circuit sub-assembly from another is well established. It is also known to use low temperature solder so as to electrically/mechanically attach a given circuit module in a manner which permits its later removal for servicing and replacement without disturbing the higher temperature solder connections or other heat sensitive features of the circuit sub-assembly. It has also been known in the prior art to combine two or more circuit sub-assemblies inside a common shield arrangement with interconnections between the sub-assemblies being made with clips, wires, etc. Although connections between circuit sub-assemblies may also have been made in the prior art through apertures in metal walls, it is not believed that such interconnections have been made through a common shield wall to which both sub-assemblies are also physically affixed.
As a non-exhaustive representative sampling of possibly relevant prior art, reference may be had to the following collection of prior issued U.S. patents:
U.S. Pat. No. 3,028,573--Stoehr (1962) PA1 U.S. Pat. No. 3,069,598--Daily et al (1962) PA1 U.S. Pat. No. 3,443,161--King (1969) PA1 U.S. Pat. No. 3,549,949--Granberry (1970) PA1 U.S. Pat. No. 3,555,168--Frykberg (1971) PA1 U.S. Pat. No. 3,571,771--Stephanson (1971) PA1 U.S. Pat. No. 3,586,753--Smith (1971) PA1 U.S. Pat. No. 3,721,746--Knappenberger (1973) PA1 U.S. Pat. No. 3,816,911--Knappenberger (1974) PA1 U.S. Pat. No. 3,987,344--Ambruoso, Sr. et al (1976) PA1 U.S. Pat. No. 4,004,194--Doerflinger et al (1977) PA1 U.S. Pat. No. 4,015,070--Theurer (1977) PA1 U.S. Pat. No. 4,218,578--Olschewski et al (1980) PA1 U.S. Pat. No. 4,313,025--Grube, Jr. (1982) PA1 U.S. Pat. No. 4,322,702--Bosch (1982) PA1 U.S. Pat. No. 4,370,515--Donaldson (1983) PA1 U.S. Pat. No. 4,388,672--Skill (1983) PA1 U.S. Pat. No. 4,393,436--Sugiura et al (1983)
Both Daily et al and King teach modular electronic circuits wherein multiple sub-assemblies are utilized and interconnected. Knappenberger '746 and Knappenberger '911 also reveal interconnections between sub-assemblies through metallic walls while Granberry and Stoehr reveal similar interconnections passing through insulating walls. Smith uses a one piece molded plastic header or retaining structure through which electrical connections may be made at one side of an isolated metallic cavity. Grube, Jr. teaches a unitary die-cast assembly for isolating and housing electrical radio circuits and Skill teaches a radio printed circuit board assembly where circuit sub-assemblies are interconnected through apertures in the insulating printed circuit board structure. Frykberg illustrates an electronic circuit housing which is divided into plural electrically isolated cavities. Stephanson teaches a two piece housing assembly. Ambruoso, Sr. et al teach a plug-in type of electronic module device for mobile radio equipment. Doerflinger et al teach a housing for electrical circuit sub-assemblies which includes electrically isolated compartments. Theurer also teaches an electrically shielded compartment for mounting an electrical circuit. Olschewski et al teach a two pieces r.f. shield having a gap between its two parts. Bosch teaches a two piece housing structure. Donaldson teaches a plural compartment electrically shielded structure for use with a printed circuit board. Sugiura et al also show a housing for electronic sub-assemblies which has multiple electrically isolated chambers formed by metallic walls in the housing assembly.
Unfortunately, none of such prior art structures have been found to provide an ideal mechanical/electrical environment for frequency synthesizer modules using VCO and PLL sub-assemblies and suitable for use in mobile radio equipment.